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UNIVERSITY  OF  ILLINOIS 


Agricultural  Experiment  Station 


BULLETIN  No.  153 


COMPARISON   OF   METHODS   OF   SAMPLING 
CREAM  FOR  TESTING 


BY  CARL  E.  LEE  AND  NELSON  W.  HEPBURN 


URBANA,  ILLINOIS,  FEBRUARY,  1912 


SUMMARY  OF  BULLETIN  No.  153 

1.  In  testing  cream,   duplicates   obtained  by  the   same   or  different   testers 
are  accompanied  by  a  reasonable  variation.     In  samples  reported  87.7  percent 
were  exact  duplicates  or  checked   within  one-half   percent,  9.8  percent  varied 
one  percent  from  the  individual,  while  2^  percent  showed  a  variation  of  more 
than  one  percent.     The  above  figures  are  significant  to  anyone  expecting  exact 
duplicate  results  each  time  a  sample  is  retested-  Pages  550-551. 

2.  There  is  a  greater  latitude  of  variation  between   composites  and   indi- 
vidual samples  than  there  is  between  two  sets  of  composites,  but  this  variation 
is  approximately  evenly  divided.  Pages  552-553,  554-555- 

3.  Of  Hepburn's  composites  36.40  percent  tested  above,  while  41.99  percent 
fell  below  the  individual.  Pages  552-553. 

4.  Two  series  of  composites  taken  in  the,  same  manner  showed  the  follow- 
ing tendency  for  variation :     63.73  percent  were  exact  duplicates,  or  varied  but 
one-half  percent;    17.60  percent  varied  i  percent;    6.33  percent  varied  1.5  per- 
cent;   7.52  varied  2  percent;    2.1  percent  varied  2.5  percent;    while  2.8  percent 
varied  more  than  2.5  percent.  Page  565. 

5.  During  the  winter  months  41.87  percent  of  the  composites  tested  lower 
than  the  individual  against  35.38  percent  testing  higher.     During  the  summer 
months  33.91  percent  tested  lower  against  43.16  testing  higher.  Page  570. 

6.  The  results  of  long  time  averages  are  seen  in  the  figures  showing  that 
during  Lee's   period   of   six   months  only   15.7  percent   of   the   samples  varied 
more  than  one-half  percent,  that  during  Hepburn's  period  15.9  percent  of  the 
samples  varied  more  than  one-half  percent,   and  that  under  the  proportionate 
system,  for  a  period  of  six  months,  24.75  percent  of  the  samples  varied  more 
than  one-half  percent.  Page  572. 

7.  Based  on  the  year  period  only  5.95  percent  of  Lee -samples  varied  more 
than  one-half  percent,  while  during  the  same  length  of  time  7.78  percent  of 
Hepburn's  varied  more  than  one-half  percent.  Page  572. 

8.  Results  from  the  yearly  average  butter  fat  show  14.52  percent  of  com- 
posites below  the  individual  and  7.7  above,  by  Lee,  and  by  Hepburn,  15.34  per- 
cent below  and  7.78  above.     These  results  are  closer  than  the  results  obtained 
by  duplicate  testing.  Page  572. 

9.  Results   are   corroborated   by  total   pounds   of   butter    fat   in   Table    16, 
showing   a   variation   between    individual    and    composite    samples    of   27  hun- 
dredths  and  16  hundredths  percent  for  Lee  and  Hepburn  respectively. 

Page  574. 


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COMPARISON  OF  METHODS  OF  SAMPLING 
CREAM  FOR  TESTING 

BY  CARL/  E.  L/EE,  ASSISTANT  CHIEF  IN  DAIRY  MANUFACTURES,*  AND 
NELSON  W.  HEPBURN,  FIRST  ASSISTANT  IN  DAIRY  MANUFACTURES 

INTRODUCTION 

For  several  years  past  butter  fat,  as  determined  by  the  Babcock 
test,  has  been  used  as  a  paying  basis  for  the  dairy  product  deliv- 
ered to  creameries ;  yet,  after  years  of  experience,  those  who  have 
watched  the  development  of  the  various  systems  of  testing  and 
sampling  are  realizing  that  many  of  those  systems  approved  or 
disapproved  by  common  consent,  may  or  may  not  be  giving  results 
which  are  mutually  satisfactory  to  both  manufacturer  and  patron. 

Since  butter  fat  is  the  basis  of  all  creamery  calculation  and,  in 
turn,  the  basis  of  payment  for  the  product  from  the  farm,  it  is  im- 
perative that  the  method,  or  methods,  followed  in  taking  samples 
and  determining  the  percentage  of  fat  be  consistent  to  a  degree 
which  will  work  hardship  neither  to  the  manufacturing  concern 
nor  to  the  patron  of  the  creamery. 

It  is  conceded  that  the  Babcock  test,  properly  manipulated,  is 
the  easiest  and  the  most  accurate  and  economical  means  in  the 
hands  of  the  creamerymen  for  testing  milk  and  cream  for  fat,  and 
that  the  points  of  dispute  and  subjects  for  popular  and  scientific 
discussion  are  more  intimately  associated  with  systems  of  sampling. 

It  is  not  the  purpose  of  this  investigation  to  advocate  any  one 
method  of  sampling  as  being  accurate  above  all  others;  for  it  is 
perfectly  clear  that  if  it  should  appear  that  any  or  all  the  systems 
give  equally  good  results,  they  would  not  all  be  applicable  to  every 
condition.  For  example :  our  larger,  and  many  of  our  smaller, 
centralizers  pay  for  each  delivery  or  shipment  of  cream.  This,  in 
itself,  presupposes  the  testing  of  every  can  of  cream  as  it  arrives, 
and  the  system  of  sampling  automatically  regulates  itself.  It  will 
further  appear  that  the  experience  of  the  operator,  the  number  of 
patrons,  and  the  business  principles  followed,  all  modify  the  test- 
ing system. 

Now  Assistant  Professor  of  Dairying",  University  of  Wisconsin 

545 

S7 


546  BULLETIN  153  [February, 

IMPORTANCE  OF  TESTING 

There  is  a  common  opinion  among  creamery  inspectors  that  test- 
ing does  not  occupy  the  prominent  place  it  should  in  creamery 
practice,  indicating  that  few  are  familiar  with  the  disastrous  re- 
sults of  careless  testing  and  practices  of  sampling  which  may  lead 
to  an  inaccurate  determination  of  butter  fat.  If  the  test  applied 
to  creamery  weights  is  to  be  used  as  a  basis  for  payment,  then 
it  bears  the  same  relation  to  that  industry  that  a  system  of  weights 
and  measures  does  to  any  commercial  business.  Few  realize  that 
the  creamery  overrun  will,  on  a.  40  percent  cream  basis,  be  in- 
creased or  decreased  3  percent  by  introducing  an  error  of  I  per 
cent  in  testing.  This  means,  in  a  plant  averaging  700  pounds  of 
butter  daily,  a  loss  or  gain  of  21  pounds  of  butter,  worth  about 
$6.00 — the  salary  of  two  gQod  men.  Thus  it  becomes  evident 
that  any  practice  resulting  in  a  test  uniformly  high  is  a  source  of 
constant  drain  to  the  plant.  Should  the  error  fall  in  the  opposite 
direction,  the  plant  must  sooner  or  later  suffer  from  a  list  of  dis- 
satisfied patrons. 

As  already  referred  to,  the  method  of  sampling  cream  for  the 
determination  of  butter  fat  has  been  a  subject  of  dispute  and 
doubt,  particularly  since  the  change  in  manufacturing  conditions 
has  led  to  the  delivery  of  a  large  amount  of  butter  fat  in  the  form 
of  cream.  The  object,  therefore,  of  this  investigation  is  primarily 
to  compare  the  efficiency  of  systems  of  sampling  now  in  use,  to 
test  their  reliability,  and  to  form  some  opinion  of  their  application 
and  relation  to  creamery  practice. 

METHODS  OF  COLLECTING  DATA 

The  data  presented  in  this  bulletin  cover  the  work  of  one  year 
in  the  creamery  operated  by  the  Department  of  Dairy  Husbandry, 
University  of  Illinois.  As  a  result  of  this  method  of  gathering 
material  several  topics  of  secondary  interest  have  presented  them- 
selves, some  of  which  seem  to  bear  a  direct  relation  to  the  subject  in 
hand.  Wherever  possible  such  influences  have  actually  been  taken 
into  account,  but  many  of  the  facts  that  appear  can  be  assigned  no 
numerical  value  and  at  best  one  may  only  call  attention  to  their 
possible  influence. 

If  the  sole  object  of  the  investigation  had  been  to  make  mere 
comparisons  on  the  various  systems  of  sampling  cream,  this  prob- 
ably could  have  been  more  successfully  and  more  scientifically  car- 
ried out  entirely  distinct  from  the  commercial  activity;  but  with 
the  secondary  object  in  view  it  seemed  best  not  only  to  compare  the 
systems  on  a  large  scale,  but  also  to  correlate  them  as  closely  as 
possible  with  modern  creamery  practice.  This  end  was  accom- 
plished, as  each  sample  represented  not  only  a  comparison  but  also 
a  can  of  cream  which  contributed  to  the  creamery's  daily  supply. 


COMPARISON  METHODS  OF  SAMPLING  CREAM  FOR  TESTING  547 

During  the  year  the  creamery  had  on  its  list  some  103  patrons 
but  the  results  published  are  on  only  77,  as  the  other  26  began  de- 
livering toward  the  end  of  the  season  and  would  not  make  fair 
comparisons  with  patrons  delivering  cream  the  whole  year.  The 
output  was,  on  an  average,  about  2500  pounds  of  butter  per  week. 

KINDS  OF  SAMPLES  TAKEN 

The  comparisons  drawn  in  the  following  data  are  between  "in- 
dividual" samples,  that  is,  samples  taken  from  each  delivery  and 
tested  at  once;  "ordinary  composite"  samples;  and  "proportionate" 
samples,  that  is,  samples  taken  in  proportion  to  the  amount  of  cream 
received.  The  composite  system  of  sampling  here  referred  to  con- 
sists merely  in  obtaining  a  sample  composed  of  representative 
amounts  of  cream  from  each  delivery  of  a  single  patron  for  a  period 
of  fifteen  days — the  method  employed  in  whole  milk  creameries. 
The  samples  were  kept  in  one-half  pint  lightning  jars  with  tin 
covers,  and  preserved  with  corrosive  sublimate,  in  tablet  form,  two 
small  tablets  being  used  during  the  hot  months  and  one  during  the 
cooler  season.  In  making  the  composite  no  effort  was  made  to  ob- 
tain a  sample  in  proportion  to  the  amount  delivered;  the  object 
being  merely  to  have  a  sample  composed  of  cream  from  each  de- 
livery at  the  end  of  fifteen  days,  as  well  as  a  sample  large  enough 
for  convenient  manipulation  in  testing.  It  may  be  added,  how- 
ever, that  this  practice,  when  averaged,  usually  results  in  securing 
amounts  of  cream  from  each  delivery  which  are  approximately 
equal  in  volume. 

Since  the  primary  object  was  to  compare  individual  and  com- 
posite sampling,  the  first  step  was  to  obtain  a  representative  sample 
of  cream  from  each  patron's  delivery.  This  was  usually  a  half 
pint  taken  from  a  can  of  cream  after  it  had  been  vigorously  stirred 
to  insure  thoro  mixing.  These  samples  were  then  tested  for  fat, 
and  composites  made  by  adding  approximately  equal  amounts  of 
cream  for  each  delivery  to  the  respective  composite  bottles;  that 
is,  if  patron  Number  One  delivered  a  can  of  cream  a  half  pint 
bottle  was  taken  for  a  sample,  tested,  and  about  one-fourth  of  it 
added  to  composite  bottle  Number  One. 

The  method  of  handling  the  proportionate  sample  varied  from 
this  only  in  that  an  effort  was  made  to  secure  samples  in  proportion 
to  the  amount  of  cream  delivered. 

DETAILS  OF  TESTING 

For  the  whole  experiment  40  percent  1 8-gram  bottles,  gradu- 
ated to  one-half  percent  were  used.  Scales  for  weighing  samples 
were  of  the  creamery  torsion  type.  The  duplicates  represent  the 
results  of  two  men  working  independently,  rather  than  the  close- 


548  BULLETIN  153  [February. 

ness  of  duplication  by  one  man.  This  offers  the  additional  ad- 
vantage of  making  it  possible  to  form  some  opinion  of  variations 
occasioned  by  two  persons  doing  the  same  testing. 

In  preparing  the  composites  for  testing  they  were  handled  in 
lots  of  24  each,  the  capacity  of  the  centrifuge.  The  samples  were 
removed  from  the  shelf  and  placed  in  rotation  in  a  pan  of  sufficient 
height  to  permit  the  addition  of  hot  water  to  the  cream  line.  After 
warming  to  fluid  condition  the  cream  and  fat  were  removed  from 
the  sides  of  the  bottles  by  means  of  a  spatula,  after  which  a  uni- 
form sample  was  obtained  by  pouring  several  times  from  one  vessel 
to  another.  An  1 8-gram  sample  was  then  weighed  into  the  test 
bottle,  after  which  the  composite  was  passed  to  the  second  tester, 
who  obtained  a  duplicate. 

Subsequent  to  the  sampling  the  testing,  with  few  exceptions, 
was  carried  on  in  the  usual  manner.  Highly  satisfactory  results 
were  gained,  however,  by  a  slight  change  in  manipulation  previous 
to  the  whirling.  This  consisted  of  filling  the  test  bottles  with  water 
to  the  base  of  the  neck,  previous  to  the  first  whirling.  Experience 
in  testing  cream  indicated  that  the  use  of  such  a  method  resulted 
in  a  larger  proportion  of  clear  tests,  and  the  absence  of  those  com- 
mon faults  described  as  curdy  samples  and  burned  fat.  It  may  be 
noted  in  this  connection  that  the  testing  of  cream,  and  especially  of 
composites,  during  the  summer  months  is  frequently  attended  by 
undesirable  results  in  the  form  of  burned  samples  or  otherwise 
cloudy  tests. 

It  will  be  noted  that  each  system  of  sampling  is  practically  a  prob- 
lem of  its  own  and  will  necessarily  be  treated  as  such  preliminary 
to  comparing  it  with  any  other  system.  In  the  general  comparison 
the  individual  sample  is  used  as*  the  basis  for  comparison. 

Since  all  the  data  are  taken  from  the  creamery  records,  the 
comparisons  appear  first  in  terms  of  pounds  of  butter  fat.  Such 
comparisons  are  interesting  from  the  standpoint  of  the  problem  of 
financial  loss  or  gain  accruing  to  each  patron,  but  they  are  not  on 
a  comparable  basis,  as  the  pounds  of  cream  for  each  patron  might 
be  widely  different.  It  thus  becomes  evident  that  a  system  of 
sampling  occasioning  a  large  number  of  pounds  variation,  in  spe- 
cial instances  might,  or  might  not,  be  the  cause  for  a  high  percent- 
age variation.  In  view  of  these  facts  it  seemed  best  to  make  a 
preliminary  study  of  each  system,  and  then  compare  it  with  the  in- 
dividual system  on  the  percentage  basis.  Since  each  composite  repre- 
sented the  test  of  a  patron's  cream  for  a  half  month,  the  individual 
samples  would  be  reduced  to  similar  terms  by  dividing  total  pounds 
of  butter  fat  for  those  fifteen  days  by  the  total  pounds  of  cream, — 
in  other  words,  determining  the  "average  test."  The  average  test, 
representing  the  individual  samples,  is  then  fittingly  compared  with 
any  composite  taken  for  the  same  length  of  time. 


/p/<?]  COMPARISON  METHODS  OF  SAMPLING  CREAM  FOR  TESTING  549 

In  each  comparison  the  "individual"  sample  is  represented  in 
the  distribution  table  by  the  average  test  and  the  comparisons  may 
be  said  to  be  drawn  in  three  forms :  First,  in  the  form  of  distri- 
bution tables  representing  all  the  tests;  second,  in  the  form  of 
distribution  tables  showing  the  effect  of  averages  on  the  distribu- 
tion; while  the  third  is  a  comparison  of  averages  expressed  in  terms 
of  pounds  of  butter  fat  obtained  by  adding  all  the  butter  fat  for 
the  year  under  each  system. 

DIFFERENCES  IN  DUPLICATES 

During  the  month  previous  to  the  beginning  of  this  experiment 
preliminary  data  had  been  collected  which  emphasized  the  sug- 
gestion that  there  is  a  uniform  variation  in  testing  duplicate  cream 
samples,  together  with  a  similar  variation  in  the  results  of  two 
persons  attempting  to  do  duplicate  work. 

The  following  distribution  table  is  a  comparison  of  the  results 
of  Lee's  and  Hepburn's  tests  on  composites  and  the  summary  is  no 
doubt  a  tangible  expression  of  the  usual  variation  that  may  be 
expected  from  two  experienced  testers  with  like  standards.  Obser- 
vations from  field  conditions,  however,  would  lead  one  to  believe 
that  the  variation  of  results  obtained  by  two  creamerymen  would 
considerably  exceed  this.  This  factor  of  variation  between  dupli- 
cate samples  or  between  two  testers  should  be  borne  in  mind  in 
drawing  other  comparisons,  as  it  must  be  evident  that  any  subse- 
quent variation  must  be  in  excess  of  this  if  it  is  to  be  attributed  to 
method  of  sampling. 

Reading  to  the  right  of  the  zero  point  gives  the  number  of  Lee's 
composite  samples  with  their  respective  percents  above  Hepburn's. 
Reading  to  the  left  gives  a  similar  comparison  below  Hepburn's, 
while  the  zero  column  represents  the  number  of  samples  in  which 
there  was  no  variation.  The  comparison  is  based  on  samples  of 
individual  patrons  for  a  period  of  one  year. 

From  the  summary  of  Table  I,  indicated  by  "total"  and  "aver- 
age percentage  variation,"  it  is  clear  that  there  is  a  slight  tendency 
on  the  part  of  Hepburn  to  test  higher  than  Lee.  This  difference 
may  be  due  to  the  use  of  different  types  of  scales  during  the  first 
five  months  of  the  comparison,  rather  than  to  any  tendency  to  read 
differently;  for  it  appeared  from  the  beginning  that,  with  respect 
to  reading,  there  was  a  remarkable  agreement  in  the  judgment  of 
the  two  testers.  This  became  more  evident  as  the  season  advanced, 
due  no  doubt  to  a  longer  experience  in  reading  and  the  further  es- 
tablishment of  a  like  standard. 


550 


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556  BULLETIN  153  [February, 

Referring  to  the  summary  of  Table  I  it  is  seen  that  87.7  percent 
of  the  1165  samples  reported  tested  the  same  or  fell  within  the  limit 
of  one-half  percent  variation,  while  there  is  only  one  instance  where 
the  difference  was  as  much  as  3  percent.  It  is  further  a  fact  worthy 
of  comment  that  the  differences  are  approximately  evenly  dis- 
tributed on  either  side  of  the  zero  line,  which  means  that  in  any 
series  of  such  tests  these  irregularities  tend  to  correct  or  at  least  to 
equalize  each  other. 

Table  2  is  a  distribution  table  used  as  a  basis  for  comparing 
Hepburn's  composite  tests  with  average  individual  tests  on  each 
patron,  for  periods  of  fifteen  days  each  during  one  year.  The  data 
are  arranged  similar  to  those  in  Table  I.  The  zero  column  shows  the 
number  of  composites  testing  the  same  as  the  average  individual 
tests.  Reading  to  the  right  of  the  zero  column  gives  the  number 
of  samples  with  their  respective  percentages  of  fat  above  the  individ- 
ual, while  those  below  the  zero  column  give  the  number  of  samples 
with  their  respective  percentages  of  fat  below  the  individual. 

In  studying  the  comparison  of  composite  with  individual  sam- 
ples it  is  at  once  obvious  that  a  much  wider  distribution  is  displayed 
than  in  the  comparison  of  duplicate  testing,  but  again,  there  is  a 
remarkable  equilibrium  of  total  results  derived  from  the  tendency 
for  the  same  number  of  samples  to  vary  an  equal  amount  in  either 
direction. 

Out  of  a  total  of  1066  samples  used  for  comparison  36.46  per- 
cent tested  higher  than  the  individual,  while  40.30  percent  fell  be- 
low the  individual,  and  57.77  percent  either  tested  the  same  or  came 
within  the  limit  of  one-half  percent  variation.  Of  the  composites 
19.22  percent  varied  one  percent  from  the  individual;  10.5  percent 
varied  1.5  percent;  5.62  percent  varied  two  percent;  while  in  6.92 
percent  there  was  a  variation  of  more  than  two  percent.  The  high- 
est variation  recorded  in  this  comparison  is  in  two  samples  differ- 
ing 4.5  percent  from  the  individual. 

Special  attention  should  be  directed  toward  the  figures  showing 
that  40.30  percent  of  the  composites  tested  lower  than  the  individ- 
uals and  only  36.46  percent  tested  above  the  individual.  While 
in  this  investigation  we  cannot  hope  to  assign  a  cause  to  such  a 
tendency,  its  presence  is  noted  in  every  comparison. 

Table  3  is  a  complement  of  Table  2  and  needs  no  explanation. 
Since  this  is  a  comparison  of  Lee's  composite  with  the  individual 
samples,  it  should  be  noted  that  there  is  the  same  degree  of  cor- 
relation between  Table  2  and  Table  3  as  between  the  comparison 
of  testers  in  Table  i. 


i<)i2\  COMPARISON  METHODS  OF  SAMPLING  CREAM  FOR  TESTING  557 

The  variation  of  Lee's  composite  from  the  individual  is  prac- 
tically the  same  as  in  the  comparison  of  Hepburn's  composite  with 
the  individual.  55.7  percent  of  the  samples  tested  the  same  or  fell 
within  the  limit  of  one-half  percent  variation ;  20.3  percent  varied 
one  percent  from  the  individual;  11.7  percent,  1.5  percent;  6  per- 
cent, 2  percent ;  while  6.39  percent  varied  more  than  2  percent.  The 
highest  variation  was  5  percent  in  one  sample. 

PROPORTIONATE  SAMPLING 

The  comparison  of  the  individual  samples  with  the  proportionate 
composite  is  on  a  slightly  different  basis  from  those  comparisons  in- 
volving individual  and  ordinary  composites,  since  the  data  covers  a 
period  of  only  six  months  and  consequently  represents  about  half 
the  number  of  samples  used  in  former  comparisons. 

The  proportionate  sample  was  taken  by  means  of  a  graduated 
pipette,  the  size  of  the  samples  varying  in  different  instances  from 
i  cc.  per  pound  of  cream  to  10  or  20  cc.  The  amount  of  cream 
usually  delivered  by  the  patron  was  the  standard  determining  the 
ratio  to  be  used,  and  the  effort  was  made  in  this  case,  as  with  the 
regular  composite,  to  have  a  sample  at  the  end  of  fifteen  days  large 
enough  to  be  convenient  for  manipulation  in  testing.  In  this  we 
were  successful  only  in  so  far  as  we  were  able  to  estimate  the 
amount  of  cream  to  be  delivered  by  a  patron  for  fifteen  days,  and 
so  it  often  happened  that  the  sample  for  the  testing  period  was 
represented  by  a  smaller  amount  of  cream  than  is  suitable  for  the 
best  results. 

Theoretically,  composites  taken  in  proportion  to  the  amount  of 
cream  should  give  results  corresponding  most  closely  to  the  in- 
dividual testing,  and  such  would  probably  be  the  case  in  sampling 
milk  or  thin  cream,  but  the  mechanical  difficulties  attending  the  use 
of  such  a  system  with  heavy  cream  tend  to  destroy  its  proportion- 
ate value,  and  with  thick,  sour,  and  viscous  cream,  such  a  sample 
often  becomes  proportionate  only  in  name.  This  perhaps  will  serve 
to  explain  the  cause  for  some  of  the  irregularities  of  the  propor- 
tionate sample  taken  in  this  manner. 

Table  4  illustrates  by  distribution  the  difference  between  pro- 
portionate composites  and  individual  samples.  In  this,  as  in  for- 
mer cases,  the  individual  is  used  as  a  standard  for  comparison. 


558 


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COMPARISON  METHODS  OF  SAMPLING  CREAM  FOR  TESTING  563 

Table  4  shows  a  still  greater  latitude  of  distribution :  viz., 
44.77  percent,  against  55.7  percent  in  the  previous  comparison, 
tested  the  same  or  varied  only  one-half  percent;  20.29  percent 
varied  I  percent;  14.31  percent,  1.5  percent;  9.16  percent,  2  per- 
cent; and  11.31  percent,  more  than  2  percent.  The  widest  variation 
was  5  percent.  Here  again,  with  44.12  percent  of  the  samples  test- 
ing below  and  36.65  percent  testing  above,  is  a  tendency  for  the 
composite  to  fall  below  the  individual.  No  doubt  the  wider  latitude 
of  variation,  as  well  as  a  greater  tendency  to  collect  on  the  low  side 
in  this  system  of  sampling,  is  largely  accounted  for  by  the  fact  that 
in  an  effort  to  secure  a  proportionate  sample  where  small  amounts 
of  cream  were  delivered,  it  often  happened  that  small  samples  were 
collected  for  testing.  This  practice  sometimes  resulted  in  samples 
which  were  too  small  for  convenient  manipulation. 

The  foregoing  distribution  table  (Table  5)  is  prepared  merely  to 
show  how  the  proportionate  composite  varied  from  Hepburn's  regu- 
lar composite.  Whether  this  comparison  w^ould  be  any  criterion  for 
the  comparative  results  of  proportionate  and  ordinary  composite 
samples  in  general,  would  depend  largely  on  how  the  proportionate 
samples  were  taken.  The  notable  feature  of  this  table  is  the  tend- 
ency of  the  proportionate  composite  to  fall  below  the  regular  com- 
posite. 

Table  6  is  the  percentage  summary  of  distribution  tables  num- 
bers i,  2,  3,  4  and  5,  compiled  here  merely  to  show  their  compara- 
tive values.  Figures  in  the  table  show  percentage  of  samples  vary- 
ing in  either  direction  from  the  zero  line  by  each  system. 


564 


BULLETIN  153 


[February, 


Table  7  is  a  comparative  expression,  in  terms  of  percent,  of  the 
variation  occasioned  by  the  methods,  with  the  individual  used  as  a 
basis  for  comparison.  Column  i  gives  the  percent  of  samples  test- 
ing the  same  as,  or  varying  one-half  percent  from  the  individual; 
column  2,  the  percent  varying  one  percent;  column  3,  the  percent 
varying  1.5  percent;  column  4,  the  percent  varying  2  per  cent;  col- 
umn 5,  the  percent  varying  more  than  2  percent.  Columns  6  and  7 
are  quite  significant  in  that  they  show  the  total  percent  of  samples 
testing  above  and  below  the  individual  and  are  consequently  the 
one  quantitative  expression  of  the  difference  between  the  various 
composites  and  their  relation  to  the  individual. 

TABLE  7. — SUMMARY    TABLE    COMPARING    THE    DIFFERENT    SYSTEMS   OF 
SAMPLING  WITH  THE  INDIVIDUAL  SYSTEM 


1 

2 

3 

4 

5 

6 

7 

Percent 
same  or 
varying 

%% 

Percent 
varying 
\% 

Percent 
varying 
1-%% 

Percent 
varying 

2% 

Percent 
varying 
more 
than  2% 

Percent 
above 

individual 

Percent 
below 
individual 

Hepburn 
with 
individual 

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19.22 

10.50 

5.62 

6.92 

36.46 

40.30 

lyee  with 
individual 

55.70 

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11.70 

6.00 

6.39 

34.30 

41.99 

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ate  with 
individual 

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20.29 

14.31 

9.16 

11.31 

36.65 

44.12 

1912}  COMPARISON  METHODS  OF  SAMPLING  CREAM  FOR  TESTING  565 

DIFFERENCE  IN  SAMPLES  TAKEN  IN  THE  SAME 

MANNER 

From  the  foregoing  data  it  is  evident  that  there  is  considerable 
difference  in  tests  resulting  from  the  various  commercial  methods 
of  collecting  samples,  which  naturally  leads  up  to  the  question  of 
how  much  variation  there  might  be  between  samples  purported  to 
be  taken  in  the  same  manner.  Such  data  would  be  especially  in- 
teresting on  the  ordinary  composite,  since  this  is  the  usual  cream- 
ery sample.  It  would  be  further  suggested  that  any  variation  ob- 
tained under  different  systems  of  sampling  should  be  in  excess  of 
this  if  it  is  to  be  attributed  to  the  difference  in  method.  As  a  means 
of  obtaining  some  idea  of  the  variation  in  samples  taken  in  a  like 
manner  two  ordinary  composites  were  collected  during  the  last 
month  of  the  experiment.  These  were  taken  after  the  manner  de- 
scribed for  collecting  the  regular  composite,  so  that  either  might 
have  been  used  as  a  paying  basis  for  the  month.  The  results  here 
showed  34.6  percent  of  the  samples  to  be  exact  duplicates;  19.08 
percent,  one-half  percent  high;  9.86  percent,  one  percent  high; 
2. 1 1  percent,  one  and  one-half  percent  high;  4.22  percent,  two  per- 
cent high;  1.4  percent,  two  and  one-half  percent  high;  and  1.4 
percent,  four  percent  high.  10.5  percent  were  one-half  below  the 
individual;  7.74  percent,  one  percent  below;  4.22  percent,  one  and 
one-half  percent  below;  2.83  percent,  two  percent  below;  0.7  per- 
cent, two  and  one-half  percent  below;  and  1.4  percent,  three  and 
one-half  percent  below. 

By  subtracting  the  variation  resulting  from  duplicate  testing, 
we  then  have  some  indication  of  the  variation  accruing  to  samples 
taken  in  the  same  manner.  This,  however,  is  perhaps  only  a  sug- 
gestion of  results,  since  the  number  of  comparisons  are  too  small 
to  warrant  any  conclusions. 

SEASONAL  INFLUENCE 

The  condition  of  composites,  together  with  some  knowledge  of 
the  causes  for  such  conditions,  is  probably  responsible  for  the  in- 
ference that  seasons  of  the  year,  accompanied  by  various  intensi- 
ties of  heat,  cold  and  light,  have  their  effect  upon  the  results  ob- 
tained from  the  composite  samples.  As  a  means  of  comparing  the 
effect  of  seasons  two  distribution  tables,  numbers  8  and  9,  are  here 
presented,  comparing  composite  with  individual  samples,  for  the 
winter  months  of  December,  January,  February  and  March,  and 
the  summer  months  of  June,  July,  August  and  September. 


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r-INrH                              rHrH                                                         MrHrH 

rH 

drHrHrH                                                                rHrHrH                rHrHrHtO 

rH 

rH         rH                MrHrHrHC<)rHrH         M          rHrH         T-trHC<lrH         CS                rH         rH 

^ 

rHrH                rH         WrON         rHtO^J-                       C-lMf<>rH         rHrH                       rH         rHrHfO 

O 

tOrHrHMMrH         t^tSrHMdCl-*         -*rH         MMMMrHrHtOrH         rH          rHrH 

Percent  below  individual 

* 

rHMrH         WrH         rHrHWMrH         rHrH                N         MtO                VO                rH         rHrH 

rH 

*^r-  ------ 

rH 

C^  M  rH  rH  rH                       rH                                                                                                                             rH 

« 

rH  rH                rH                                                                                                                      rH          rH 

N 

rH                                                                       rH         rH 

to 

rH 

to 

- 

5 

- 

rH 

Patron 
number 

1912}  COMPARISON  METHODS  OF  SAMPLING  CREAM  FOR  TESTING 


569 


rHCOrHCJrHOlrHrHf^ 


rH  rt  rfr  f<3  N  rH 


rH          rH  <<J  n  rH  C<»  N          rHrHrHIO 


a 


t<)         ClrHMrHrH«rOrH 


g 


570 


BULLETIN  153 


[Februarv 


P 

00 

w 

o 


Percent  above  individual 

10 

IO 
W 

^ 
•* 

•* 

•*•  00 

<SJt> 

* 

co 

CM  00 

l>  t^ 

co 

3% 

i—  i  rH 

* 
« 

00  CO 
0  CO 

rH  N 

W 

vo  •* 

rH  rH 

ri  •* 

a? 

rH 

%S 

rf  VO' 

rH 

t^  CO 

vo  •* 

00  M' 

rH 

« 

oo  ON 

CO  **• 

VO  '*' 

rH  rH 

O 

iO  I> 

in  10 

M'  CO 
CN  M 

Percent  below  individual 

* 

0«> 

rH  \T> 

i>  ^6 

rH  rH 

rH 

38 
N  t>; 

rH 

* 

rH 

f>l  00 
C4  rH 

l>  1C 

CJ 

O  O\ 
^J-  iO 

ri  ci 

* 

M 

•*  o 
"^  °°. 

rH  rH 

CO 

10  N 

O\  iO 

* 

f~> 

^J- 

fM 

"t 

9 

^ 

Tj- 

iO 

Winter  months 
Summer  months 

a 


. 


c 

n3 
00 


V 

^     O  rH 

•£  re  3 

SH           *O 
£)#)•»-< 

O       *U        r> 

00  VO 
CO  rH 

a 

MH     O  »-« 

O  *fl>  ™ 

|  cc-| 

00  O\ 

III 

rH  co' 
•*  CO 

in 

*R^ 

III 

vo  t> 

INFLUENCE 

•ercent 
riation 

VO  CO 

11.—  SEASONAL 

rV  « 

N  > 

percent 
iriation 

iO  O 

10  rH 

rH  CJ 

w 

r^> 

rH  rH 

n 
<! 

rH 

C    0 

D.S 

23 

rH  CO 

rl   ffl 

0*^' 

rH    > 

Same  or 
^  percent 
variation 

CO  CO 

O  vo 

vo'  •* 

months 
;rmonths 

Winter 
Summ< 

1912} 


COMPARISON  METHODS  OF  SAMPLING  CREAM  FOR  TESTING 


571 


Table  n  is  also  derived  from  Tables  8  and  9,  illustrating  still 
further  the  comparative  relation  between  composite  and  individual 
samples  collected  during  the  two  extreme  seasons  of  the  year. 

The  study  of  seasonal  influence  is,  in  this  connection,  of  pe- 
culiar interest,  since  the  question  of  difference  caused  by  season  is 
intimately  related  to  influences  of  evaporation  and  other  factors 
potent  in  causing  disagreement  between  composites  and  individu- 
als. Referring  to  Table  n,  we  note  a  tendency  for  the  composite 
to  fall  below  the  individual  in  winter,  with  more  than  a  correspond- 
ing tendency  for  a  higher  test  in  summer. 

RESULTS  OF  AVERAGES 

Tables  12  and  13  are  summary  tables  derived  from  data  re- 
corded under  Table  16,  which  gives  total  butter  fat,  cream,  and 
average  tests  by  patrons  under  each  system  of  sampling  for  six 
months  and  for  one  year.  It  might  be  added  that  the  object  of  in- 
serting the  six-months  comparison  is  to  show  data  comparable 
with  the  proportionate  samples,  since  they  were  collected  only  for 
that  length  of  time. 

TABI.E   12.— COMPARISON  OF   COMPOSITE  WITH    INDIVIDUAL    TESTING    FOR 

Six  MONTHS 


2^ 

2 

1#- 

1 

% 

0 

X 

1 

IK 

2 

1Yz 

Number  of  variations 

according  to  L<ee 

2 

2 

7 

22 

60 

13 

6 

1 

Percentage   variation 

according  to  L/ee 

1.7 

1.7 

6.2 

19.5 

53.7 

11.5 

5.30 

.8 

Number  of  variations 

according  to  Hepburn 

2 

2 

7 

11 

70 

16 

5 

1 

Percentage    variation 

according  to  Hepburn 

1.75 

1.75 

6.13 

9.64 

61.4 

14. 

4.4 

.87 

Number  of  variations 

according  to  "propor- 

tionate" 

1 

2 

2 

19 

20 

52 

12 

4 

Percentage   variation 

according  to  "propor- 

tionate" 

.9 

1.77 

1.77 

16.81 

17.61 

46.01 

10.62 

3.6 

Tables  12  and  13  show  the  distribution  of  the  average  tests, 
\vith  a  marked  tendency  for  agreement  of  the  various  systems.  It 
is  apparent  that,  disregarding  the  proportionate  sample,  average  re- 
sults for  comparatively  long  periods  show  no  more  difference  be- 
tween the  various  systems  than  exists  between  duplicate  samples. 

Table  15  is  still  further  summarized  in  Table  14  (A  and  B), 
showing  the  percent  of  samples  testing  the  same  or  varying  only 


572 


BULLETIN  153 


[February, 


one-half  percent,  one  percent,  one  and  one-half  percent,  and  two 
percent.  Attention  should  again  be  directed  to  the  two  columns 
showing  the  percent  of  composites  above  and  below  the  individual, 
since  this  is  a  quantitative  record  of  the  percentage  difference 
based  on  pounds  of  butter  fat  delivered  by  patrons  for  the  six- 
months  period  and  for  the  yearly  period. 


TABL.E  13. — COMPARISON   OP    COMPOSITE    WITH    INDIVIDUAL,   TESTING    FOR 

ONE  YEAR 


2y2 

2 

1# 

1 

% 

0 

* 

1 

IK 

2 

2Y2 

Number  of  variations 

according  to  L/ee 

1 

1 

5 

10 

91 

9 

Percentage  variation 

according-  to  L/ee 

.85 

.85 

4.27 

8.55 

77.8 

7.7 

Number  of  variations 

according  to  Hepburn 

1 

4 

3 

10 

90 

8 

1 

Percentage   variation 

according  to  Hepburn 

.85 

3.39 

2.56 

8.54 

76.92 

6.83 

.85 

TABLE    14. — SUMMARY    TABLE    SHOWING    PERCENTAGE    DIFFERENCE    OF 

VARIOUS  COMPOSITES  COMPARED  WITH  THE  INDIVIDUAL.    RESULTS 

DERIVED  FROM  POUNDS  BUTTER   FAT  DELIVERED 

(A)     Based  on  a  Period  of  Six  Months 


Same  or 
%  per  c«nt 
variati'n 

1  per 
cent 
variati'n 

1%  per 
cent 
variati'n 

2  per 
cent 
variati'n 

Below 
individ- 
ual 

Above 
individ- 
ual 

L/ee 

84.70$ 

11.6$ 

2.50$ 

1.70$ 

29.10$ 

17.60$ 

Hepburn 

85.04$ 

10.53$ 

2.62$ 

1.75$ 

19.27$ 

19.27$ 

Proportionate 

84.24$ 

20.41$ 

1.77$ 

1.77$ 

38.86$ 

14.22$ 

(B)     Based  on  a  Period  of  One  Year 


L/ee 
Hepburn 

94.05$ 

92.29$ 

4.27$ 
3.41$ 

0.85$ 
3.39$ 

0.85$ 
0.85$ 

14.52$ 
15.34$ 

7.70$ 
7.69$ 

The  above  table  still  further  emphasizes  the  tendency  for  varia- 
tion of  results  to  equalize  each  other,  especially  at  the  end  of  long 
periods  of  time,  indicating  clearly  that  there  is  very  little  difference 
in  the  various  methods  of  sampling  when  results  are  compared  for 
a  season. 


1912] 


573 


The  following  tabulated  data  on  three  patrons,  representing  the 
pounds  of  butter  fat  for  the  year  and  half-year,  for  each  fifteen 
days,  are  presented  in  corroboration  of  former  data  and  as  an  ex- 
ample of  the  derivation  of  results  in  former  tables  based  on  the  77 
patrons.  These  are  typical  results,  selected  at  random,  and  are 


quite  representative  of  what  was 
shown  in  the  various  distributions. 


found  in  the  other  74,  as  is 


TABI,E  15. — SHOWING  COMPARISON  IN  TERMS  OF  POUNDS  OF   BUTTER  FAT 


Patron 
number 

Total  %.  mo.  deliveries  for  6  mo. 
period 

Total  Y2  mo.  deliv- 
eries for  yr.  period 

Method  of 
sampling 

Pounds 
cream 

Pounds 
(at 

Average 
test 

Pounds 
cream 

Pounds 
fat 

Average 
test 

Individual 

1019.5 

275.89 

27.06 

2808.5 

746.79 

26.59 

First  half  of 

L/ee's  composite 

276.68 

27.13 

748.54 

26.65 

month 

Hepburn's     " 

277.19 

27.19 

748.99 

26.67 

Proportionate 

269.45 

26.43 

2- 

Individual 

897 

163.31 

18.21 

2605 

661.58 

25.39 

Second  half  of 

L/ee's  composite 

162.00 

18.06 

660.29 

25.34 

month 

Hepburn's     " 

163.20 

18.19 

662.35 

25.42 

Proportionate 

161.05 

17.95 

Individual 

375.5 

126.97 

33.80 

629 

228.66 

36.40 

First  half  of 

Lee's  composite 

130.78 

34.80 

228.71 

36.40 

month 

Hepburn's     " 

131.23 

35.00 

229.22 

36.5 

Proportionate 

128.39 

34.20 

Individual 

178 

63.41 

35.60 

465 

178.77 

38.40 

Second  half  of 

L/ee's  composite 

60.90 

34.20 

174.25 

37.50 

month 

Hepburn's     " 

61.10 

34.30 

173.82 

37.40 

Proportionate 

61.76 

34.70 

Individual 

603.5 

131.63 

21.80 

1335.5 

236.50 

17.70 

First  half  of 

L/ee's  composite 

132.37 

21.95 

234.09 

17.55 

month 

Hepburn's     " 

132.79 

22.00 

235.43 

17.60 

Proportionate 

129.09 

21.4 

56- 

Individual 

471 

92.98 

19.70 

1124.15 

307.90 

24.80 

Second  half  of 

L/ee's  composite 

93.49 

19.85 

311.90 

25.10 

month 

Hepburn's     " 

93.33 

19.80 

312.22 

25.20 

Proportionate 

98.63 

20.9 

574 


BULLETIN  153 


[February 


Table  16  is  a  summary  showing  the  total  number  of  pounds  of 
butter  fat  for  each  system  of  sampling  and  testing  for  six  months 
and  for  one  year. 

TABLE  16. — SUMMARY  IN  TERMS  OF  TOTAI,  FAT 


Total  for  six  months 

Total  for  one  year 

Individual 

L<ee's 
composite 

Hepburn's 
composite 

Propor- 
tionate 

Individual 

L/ee's 
composite 

Hepburn's 
composite 

18508  Ibs 

18455  Ibs 

18487  Ibs 

18344  Ibs 

48233  Ibs 

fflOS  Ibs 
\l 

4^156  Ibs 

. 

Pounds 
difference 

53.05 

20.45 

164^02 

128.34 

76.95 

Perc  '  tage 
difference 

.28 

.11 

.88 

.27 

.16 

Table  16  is  a  striking  illustration  of  the  tendency  for  variation 
to  equalize  under  the  various  systems  of  sampling.  It  should  be 
noted  here  also  that  pounds  of  butter  fat,  by  any  system  of  com- 
posites, fall  slightly  below  the  individual,  but  that  from  the  com- 
mercial point  of  view  the  yearly  percentage  difference  is  not  worthy 
of  comment. 

On  600  pounds  of  butter  fat,  a  high  yearly  estimate  for  the 
patrons  referred  to,  the  difference  for  the  year  would  amount  to 
1.62  pounds  of  butter  fat  by  Lee  and  one  pound  by  Hepburn. 

CONCLUSIONS 

1.  Reasonable  allowance  should  be  made   for  difference   in 
duplicate  samples  tested  by  the  same  or  different  testers. 

2.  In  testing  cream  there  is  a  marked  tendency  for  variation 
between  composite  and  individual  testing  for  short  periods  of  time, 
but  the  distribution  of  this  variation  is  such  as  to  occasion  very 
small  amounts  of  difference  when  figured  on  seasonal  periods. 

3.  Composite  samples  tend  to  test  slightly  higher  than  individ- 
ual samples  in  summer,  and  lower  in  winter. 

4.  Based  on  yearly  averages  there  is  practically  no  difference 
between  composite  and  individual  samples. 

5.  Testing  in  creamery  practice  should  be  accorded  a  place  of 
prominence  commensurate  with  the  importance  of  the  results  to 
be  derived  from  it. 


• 


-. 


*-j 


UNIVERSITY  OF  ILLINOIS-URBANA 

Q.630.7IL6B  C001 

BULLETIN.  URBANA 
153-1651912-13 


30112019528428 


•llui 


JL 

r 

*w4 


.' 


